The invention relates to laser cutting machines for producing parts from sheet stock, and the invention specifically relates to detection of interference between parts and the laser nozzle and the protection of the nozzle from possible damage.
In a coordinate laser cutting machine, the elements are in arrangement very similar to those of automatic coordinate punch presses for operating on sheet stock. Namely, sheet material is moved in response to a numerical control unit in a horizontal plane in X and Y directions and maneuvered beneath a cutting head. In a punch press, a die set is actuated in the vertical direction to blank parts out of the sheet stock. However, in laser cutting machine, a power laser beam is ducted through a light pipe system to a vertical nozzle and focus device to concentrate the beam on the workpiece materialand scribe the shape. The nozzle is actuated in the vertical direction by an offset piston and is brought into proximity with the workpiece when it is desired to begin the lasing operation. In at least one prior art machine, the nozzle has a plurality of balls at its end face, which rest on the sheet stock. The nozzle is surrounded by a ring which rides on the sheet material surface, and is yieldably supported by the nozzle so that undulations and slight surface imperfections may ride underneath the ring as well. In the prior art device, the ring is provided with a chamfer about its external circumference so that a lead-in is provided for a surface imperfection or a previously cut workpiece which may be slightly disturbed from the plane of the sheet material.
It is known in lasing art to provide small tabs of uncut material, typically in the nature of 0.010 to 0.030 in. (0.2-0.8 mm) wide, which bind an essentially finished workpiece to the parent sheet stock until the sheet stock is removed from the machine. After such removal, the workpieces are easily taken from the sheet stock by breaking the tabs which retain the part in position.
Applicant has observed that, since the placement and number of tabs is generally an arbitrary process, in some cases it is possible for a workpiece to become jostled or tilted from the plane of the sheet stock and proceed along in this orientation towards the laser nozzle when another workpiece is to be cut out by the lasing head. In such case, if the rise of the disturbed workpiece is higher than the chamfer of the outer nozzle ring, jamming may take place which may result in undesirable several conditions: the laser nozzle may be crushed or disturbed from its alignment with the machine; or the entire sheet stock may be skewed and thrown into misalignment with the nozzle.
Applicant has obviated the difficulties inherent in the prior art device by an improved apparatus for controlling workpiece misalignment for parts cut from sheet stock on a lasing machine.
It is therefore an object of the present invention to provide apparatus for interference detection on a laser cutting machine.